In typical conventional steam turbine plants, steam from a boiler is fed through a steam valve apparatus to a steam turbine. Steam after having performed mechanical work in the steam turbine is circulated to return to water by a steam condenser and is boosted and supplied again to a boiler by a feed water pump. The steam valve apparatus includes a main throttle valve and a steam control valve arranged on the downstream side of the former valve. The main throttle valve can instantly stop steam which flows into the steam turbine if an emergency occurs in the steam turbine, etc. The steam control valve controls the vapor flow rate of steam supplied to the steam turbine.
In several steam valve apparatuses, a main throttle valve and a steam control valve are integrated together to form a pair. For such integration, various combinations have been proposed. For example, in a known apparatus, a main throttle valve and a steam control valve are integrated through an intermediate flow-channel part, are each mounted longitudinally (vertical mount), and are configured to be driven by an oil cylinder provided in an upper side in a casing.
In a steam valve apparatus as described above in which a main throttle valve and a steam control valve are integrated through an elbow-shaped intermediate flow channel, centrifugal force acts to drive steam toward the outside of elbow-shaped curvature when steam coming out of the main throttle valve flows inside the intermediate flow channel.
The steam after passing the intermediate flow-channel part collides, as a jet stream additionally urged by centrifugal force and flow inertia, into inner walls of a valve cap and inner walls of a casing present in an extended direction of the curvature. Since the direction of the jet stream includes a lot of upward components (i.e., components in directions opposite to directions toward the side of a valve seat (outlet side)), the jet stream follows a flow route (trajectory) in which the flow direction is abruptly changed toward the valve seat (outlet side) of the steam control valve after the collision.
In such a structure in which a main throttle valve and a steam control valve are integrated through an elbow-shaped intermediate flow-channel part, a smooth flow of steam cannot be attained, and further, an energy loss caused when a steam flow which has passed an intermediate flow-channel part is jetted to collide becomes fatal so as to cause an energy loss of a steam valve apparatus.
Under the circumstances, it is desired to provide a steam valve apparatus capable of reducing the pressure loss at the time of opening a valve of the steam valve apparatus.